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Catalytic Site Atlas

CSA LITERATURE entry for 1lcb

E.C. namethymidylate synthase
SpeciesLactobacillus casei (Bacteria)
E.C. Number (IntEnz) 2.1.1.45
CSA Homologues of 1lcbThere are 136 Homologs
CSA Entries With UniProtID P00469
CSA Entries With EC Number 2.1.1.45
PDBe Entry 1lcb
PDBSum Entry 1lcb
MACiE Entry M0031

Literature Report

IntroductionThymidylate synthase is an essential enzyme for the denoVo synthesis of dTMP, a nucleotide required for DNA synthesis, and therefore, it is an important drug target. It is a bisubstrate enzyme in which the cofactor, CH2 H4 folate, serves as both the one-carbon donor to the substrate dUMP and, subsequently, as the reductant. A one-carbon unit and hydride are transferred from different sites on the cofactor, and large contributions to the catalytic power of TS are achieved through the dynamic alignment and realignment of reactants at these chemical steps.
MechansimCys198 initiates a nucleophilic attack on the ene carbon of dUMP in a Michael (1,4) addition reaction. It is polarised by Arg218. The oxyanion formed deprotonates water, which in turn deprotonates Glu60. Glu60 deprotonates water, which deprotonates the hydroxyl group, which initiates a nucleophilic attack upon the activated methylenetetrahydrofolate at the CH2=N carbon. Tyr146 deprotonates water, which deprotonates the carbon newly connected to the methylenetetrahydrofolate. This causes the formation of a C=C and the oxyanion formed deprotonates water, which in turn deprotonates Glu60. Glu60 deprotonates water, which deprotonates the hydroxyl group, eliminating the negatively charged dihydrofolate. The negatively charged nitrogen of dihydrofolate eliminates a hydride ion, which adds to the CH2=C group of the covalently attached methyl-dUMP, causing the elimination of Cys198.
Reaction

Catalytic Sites for 1lcb

Literature References

Notes:
Finer-Moore JS
Lessons and conclusions from dissecting the mechanism of a bisubstrate enzyme: thymidylate synthase mutagenesis, function, and structure.
Biochemistry 2003 42 248-256
PubMed: 12525151
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